Polyphase fuse with blown fuse indicator in each phase

ABSTRACT

A fuse, and more particularly a polyphase fuse, having a casing, or housing of insulating material is provided with a blown fuse indicator housed in a sub-housing which is an integral part of the casing, or housing proper being formed by an internal projection of the front wall of the latter.

United States Patent 1 1 1 1 3, 64,949

Swain Oct. 9, 1973 1 POLYPHASE FUSE WITH BLOWN FUSE [56] References Cited INDICATOR IN EACH PHASE UNITED STATES PATENTS [75] Inventors: Kenneth W. Swain, Box 37, 3,593,251 7/1971 Wilson 337/186 Hampton Falls, N.H. 03844; Keith 3,535,668 10/1970 Cinquin 337 244 3,391,369 7/1968 Kozocka 337/244 g gg walker 3,319,027 5/1967 Hitchcock.... 337/244 ux 2,417,268 3/1947 Powell 337/244 [73] Assignee: TheChase-Shawmut Company,

Newburyport, Mass. by said Swain; Primary Exam'inerHarold Broome General Electric Company, by said Assistant Examiner-F. E. Bell Klein. Attorney-Erwin Salzer [22] Flled: Oct. 28, 1971 [57] ABSTRACT pp 193,596 A fuse, and more particularly a polyphase fuse, having a casing, or housing of insulating material is provided [52 US. Cl. 337/244 with a blow" fuse ihdicah" hOused in a Shh-musing 51 Int. Cl. HOlh 85/30 which is an integral P of the casing husihg 58 Field of Search 337/5, 148, 241, PYPer being harmed by an internal Pmjhchm1 of the front wall of the latter.

7 5 Q iH LPIEE EE E EPE PATENTEU 9 I973 BYWWMM W, YWMM POLYPI-IASE FUSE WITH BLOWN FUSE INDICATOR IN EACH PHASE BACKGROUND OF THE INVENTION A blown fuse indicator is often a necessary addition to an electric fuse. For reasons of economy a blown fuse indicator should be as simple as possible, and include as few parts as possible. This requirement is particularly important in polyphase fuses which include generally three fuse units of which each needs a separate blown fuse indicator. This invention refers to a fuse including a blown fuse indicator of greater simplicity than prior art blown fuse indicators, and lends itself particularly well for polyphase fuses.

SUMMARY OF THE INVENTION I An electric fuse embodying this invention includes a pair of parallel conductor strips, and fuse link means conductively interconnecting the pair of conductor strips. The aforementioned fuse link means are embedded in a pulverulent arc-quenching filler. The fuse further includes a casing of insulating material defining a chamber housing said pair of conductor strips, said fuse link means and said filler. One well of said casing forms an integral hollow projection of progressively decreasing diameter extending into said chamber and being unsupported at the innermost end thereof. Said hollow projection has a rounded apex portion and a relatively small aperture at the innermost end thereof. Said wall of said casing further has a relatively large aperture juxtaposed to and aligned with said relatively small aperture. A spring biased blown fuse indicator is arranged inside said relatively large aperture in said one wall of said casing and inside said hollow projection thereof in the space between said relatively small aperture and said relatively large aperture. Fusible restraining means for said blown fuse indicator interconnect conductively said pair of conductor strips and extend through said relatively small aperture into said hollow projection of said one wall of said casing.

BRIEF DESCRIPTION OF DRAWINGS FIG. I is a somewhat diagrammatic isometric view of a polyphase fuse embodying this invention as seen from the rear end, or cover end, thereof;

FIG. 2 is a plan view ofa fuse link forming part of the structure of FIG. 1;

FIG. 3 is a vertical section across the structure of FIG. 1 taken at right angles to the front surface and to the rear surface of the structure of FIG. I; and

FIG. 4 is a section along lV-IV of FIG. 3.

DESCRIPTION OF PREFERRED EMBODIMENT Polyphase fuses are fuses wherein a plurality of fuse units are enclosed in a common casing or housing. Each of the fuse units is intended to be inserted into one phase of a polyphase circuit. Polyphase fuses are often applied for back-up protection of other circuitinterrupting devices, i.e., to protect other circuit interrupting devices on occurrence of major fault currents exceeding their interrupting capacity.

The polyphase fuse shown in the drawings to illustrate this invention is of particular compactness. The features by which its compactness is achieved are not our invention and are claimed in the copending patent application Ser. No. 96,110; filed l28-70 for COM- PACT POLYPI-IASE FUSE.

Referring now to the drawings, numeral 1 has been applied to generally designate a substantially prismatic housing or casing of electric insulating material subdivided by internal partitions 1a into three separate chambers, or compartments, llb, each closed at all sides thereof except one side, or except its rear side R. Casing 1 is preferably a molding of an appropriate synthetic resin. The three chambers lb are filled with a pulverulent arc-quenching filler, preferably quartz sand. Reference numeral 2 has been applied in FIGS. 3 and 4 to indicate this body of pulverulent arcquenching filler. Cover means 3 are provided for closing the open sides of chambers, or compartments, 1b. Cover means 3 are provided with partitions 3a arranged in registry with the partitions la of casing, or housing, I. In other words, each of partitions 1a and each of partitions 3a are arranged in a common vertical plane. The partitions 3a in cover 3 subdivide the latter into three separate chambers, or compartments, 3b of which each communicates with but one of chambers, or compartments, 1b, and is separated from all other chambers, or compartments, 1b. The body of pulverulent arc-quenching filler 2 in each of chambers, or compartments, 1b extends into one of the chambers, or compartments, 3b defined by cover 3. As a result of this geometry housing 1 and cover 3 define jointly three separate chambers 1b,3b of which each is filled with a separate body of pulverulent arc-quenching tiller 2. Cover 3 is screwed to housing 1 by four screw-threaded studs 4 shown in FIG. 1.

A pair of straight conductor strips 5 is arranged in each of chambers, or compartments, lb. Each pair of conductor strips 5 is arranged at opposite surfaces of chambers 1b and extends from the open or rear side of chambers, or compartments, lb to the side thereof opposite t0 the open side, which side is the front side of the polyphase fuse structure. The ends 5a of conductor strips S adjacent cover 3 are bent out of the plane of the remaining part of strips 5, and are intended to form terminals for connecting the polyphase fuse into a polyphase circuit. In FIG. 1 but the inside of one of the three chambers 1b is fully shown, and but one pair of conductor strips 5 is fully shown. The internal arrangement of parts is the same in all three chambers 1b and the conductor strips 5 in all three chambers are supposed to have bent ends to be used as terminals, or connectors. Conductor strips 5 are held in position by means of screws 6 projecting through the top wall and through the bottom wall of easing, or housing 1. The outer ends of screws 6, i.e., the heads thereof, may be covered with an insulating material or sealing material to preclude physical contact with any part, or parts, which have a potential above ground potential. These including seals have not been shown in the drawings.

A plurality of ribbon fuse links 7 interconnects conductively each pair of conductor strips 5. Fuse links 7 are embedded in arc-quenching filler 2. The length of each fuse link '7 exceeds the spacing between the pair of conductor strips 5 which are conductively interconnected by it, and each of fuse links 7 encloses acute angles a with the conductor strips 5 which are conductively interconnected by it. The conductor strips 5 in each of chambers, or compartments, 1b are conductively interconnected by two groups of fuse ribbon links 7. Each group of fuse links 7 includes a plurality of fuse links, i.e., three fuse links 7. The constituent fuse links 7 of each group have the same slant. The constituent fuse links of one of said two groups of fuse links 7 have a slant differing from the slant of the constituent fuse links 7 of the other of said two groups. The constituent fuse links 7 of one group slant downwardly from the rear side R of each chamber, or compartment, lb to the front side F thereof, and the constituent fuse links 7 of the other group slant upwardly from the rear side R of each chamber, or compartment, 1b to the front side F thereof. In other words, the rear ends of one group of fuse links 7 are at the level of a top conductor strip 5, and the rear ends of the other group of fuse links are at the level of a bottom conductor strip 5. The front ends of the first mentioned group of fuse links 7 are at the level of a bottom conductor strip 5, and the front ends of the last mentioned group of fuse links are at the level of a top conductor strip 5. Ribbon fuse links 7 pertaining to different groups are separated relatively far from each other, thus minimizing the danger of merger of fulgurites taking the place of fuse links 7 upon blowing of the polyphase fuse. As shown in FIGS. 1 and 3 there is a cross-over region of the fuse links 7 pertaining to one group of fuse links 7 with the fuse links 7 pertaining to the other group of fuse links. While the spacing between the constituent fuse links 7 of the two groups of fuse links is smallest at this cross-over region, the dielectric recovery of the arc gaps formed upon blowing of the polyphase fuse is satisfactory under the most adverse interrupting conditions on account of the length of the fuse links and the wide spacing of both groups of fuse links 7 along the preponderant portion of their length.

Each group of fuse links comprising three fuse links 7 is formed by one single integral stamping of sheet metal (silver) which includes a pair of parallel bars 7a of sheet metal of which each is conductively connected to one of a pair of conductor strips 5 in one of chambers, orcompartments, 1b. The stamping further includes a plurality of parallel ribbon sections 7 of sheet metal having a length exceeding the spacing of a pair of bars 7a and enclosing acute angles with bars 7a. FIG. 2 shows such a stamping including bars 7a and ribbon fuse links 7.

Each conductor strip 5 is provided with a pair of grooves 5a extending parallel to the edges of conductor strips 5. The grooves 5a of each pair of strips 5 are arranged on the juxtaposed surfaces of the former and the stampings of HG. 2 are inserted into pairs of juxtaposed grooves 5a in conductor strips 5.

Cover 3 is provided with three apertures 30 for filling the three chambers, or compartments, 1b,3b formed by housing or casing 1 and by cover 3 with pulverulent arc-quenching filler. Each aperture 3c is sealed by a plug 8 which may be formed by a cured synthetic resin, e.g., an epoxy resin.

The front side F of housing, or casing, 1 is provided with three cavities or apertures 10 having a relatively large diameter. The front wall of housing 1 forms integral hollow projections 1d each having more or less the shape of a frustum of a cone and each extending into one of chambers, or compartments, 1b. The aforementioned hollow projections 1d are preferably in the shape of solids of revolution, and each projection ld has a relatively small aperture 1e at the innermost end thereof, i.e., at the endthereof projecting farthest into one of chambers, or compartments, lb. A spring biased blown fuse indicator is arranged inside of each cavity or aperture 10 and inside each hollow projection 1d in the space between apertures 10 and 1e. The blown fuse indicator includes indicating button 9, helical biasing spring 9a, spring supporting cap 9b, and tie rod 9c. One end of spring 9a acts against button 9 and the opposite end thereof rests against cap 9b. Tie rod has an axially outer end affixed to indicating button 9 and an axially innerend which is flattened and arranged inside of hollow projection 1d. As is apparent from FIG. 3 the latter has a much larger cross-sectional area at the supported end than at the non-supported end thereof, and the latter end is closed except for the small perforation or aperture 1e therein. Reference numeral 10 has been applied to indicate a restraining wire conductively interconnecting conductor strips 5. Restraining wire 10 is substantially V-shaped and the converging end thereof extends through aperture 1e into hollow projection 1d and is threaded through a hole provided in the axially inner flattened end of tie rod 90. The aperture la in hollow projection id is sealed by a body of sealing paste which retains its paste-like consistency. Silicone grease is the preferred sealing paste since relatively high temperatures may occur at the location of aperture 1e.

Housing, or casing, 1 forms an assembly jig or fixture for assembling the parts intended to be arranged therein. First the conductor strips 5 are inserted into housing 1 and firmly held in position therein by screws 6, or other appropriate fastening means. Thereupon the stampings 7,7a are inserted into the grooves 5a of strips 5, and solder in paste form is inserted into the grooves 5a, which makes the assembly ready for induction soldering. During this process the casing 1 remains relatively cool, and the generation of heat occurs primarily at the location where it is intended to form solder joints. Thereupon some silicone grease is placed adjacent the apex of projection 1d on the inner surface thereof, and parts 9,9a, 9b and 9c are moved into place, and the ends of restraining wire 10 are threaded through the aperture 1e in projection 1d. The ends of restraining wire 10 may be affixed to conductor strips 10 by means of screws 11. Then cover 3 is attached to housing, or casing, l by means of screw threaded studs 4, and quartzsand 2 is filled into the three chambers, or compartments, lb,3b through the apertures 3c in cover 3. Finally apertures 30 are filled by sealing means 8.

This way of assembling polyphase fuses is superior to the more conventional way involving the insertion of pre-assembled fuse units, one for each phase, into a common casing or housing for the polyphase fuse. The aforementioned prior art method of insertion of preassembled fuse units each into a separate chamber of a common casing, or housing, requires the addition of spacing means between the pair of spaced conductor strips of each phase unit. Deletion of additional spacing means for the conductor strips decreases significantly the cost of manufacture since it reduces both the cost of material and of labor.

It will be apparent from the above that in the structure which has been disclosed, the casing, or housing, 1 forms the spacing means for spacing pairs of conductor strips 5, thus dispensing with the need of providing additional spacing means for each pair of conductor strips 5.

Upon blowing of the fuse fulgurites take the place of ribbon fuse links 7, causing a voltage to appear across strips 5. As a result, restraining wire fuses and pins 9 are propelled forwardly by spring action.

It will be apparent from the above that the polyphase fuse shown integrates three fuse units of which each has a substantially prismatic housing. The housing has a rear wall, a pair of substantially parallel side walls, a pair of substantially parallel top and bottom walls and a front wall. The latter has a cavity 1c and a hollow projection 1d aligned with said cavity and extending into the interior of the housing. Cavity 1c and projection 1d jointly form a blown-fuse-indicator-receiving chamber. Fastener means 6 secure one of conductor strips 5 to the top wall and the other of conductor strips 5 to the bottom wall of the housing. Conductor strips 5 are maintained in spaced relation by virtue of the spacing action of fastener means 6 and the spacing action of the aforementioned substantially parallel side walls of the casing. Additional spacers for conductor strips 5 arranged within the space bounded by the juxtaposed surfaces of conductor strips 5 are dispensed with. As a result, the entire space available between the juxtaposed surfaces of conductor strips 5 is available for fuse link means and for pulverulent arc-quenching filler.

We claim as our invention:

1. An electric fuse including a. a pair of substantially parallel conductor strips;

b. fuse link means conductively interconnecting said 'pair of conductor strips;

0. a pulverulent arc-quenching filler embedding said fuse link means;

d. a substantially prismatic casing of insulating material defining a chamber housing said pair of conductor strips, said fuse link means and said filler, one wall of said casing forming an integral hollow projection of progressively decreasing diameter extending in cantilever-like fashion into said chamber and being unsupported at the innermost end thereof, said hollow projection having a rounded apex at said innermost end thereof provided with a relatively small aperture, said one wall of said casing having a relatively large aperture juxtaposed to and aligned with said relatively small aperture;

e. a spring-biased blown fuse indicator arranged inside said relatively large aperture of said one wall of said casing and inside said hollow projection thereof in the space between said relatively small aperture and said relatively large aperture; and

f. fusible restraining means for said blown fuse indicator conductively interconnecting said pair of conductor strips and extending through said relatively small aperture into said hollow projection of said one wall of said casing.

2. An electric fuse as specified in claim 1 wherein said relatively small aperture in said hollow projection is sealed by a body of sealing paste.

3. An electric fuse as specified in claim 2 wherein said relatively small aperture in said hollow projection is sealed by a body of silicone grease.

4. An electric fuse including a. a substantially prismatic housing of electric insulating material having a front wall, a rear wall, and a pair of substantially parallel side walls and a pair of substantially parallel top and bottom walls, said front wall having a cavity and a hollow projection integral with said front wall aligned with said cavity extending in cantilever-like fashion into the interior of said housing and being unsupported at the end thereof remote from said cavity, said hollow projection having a relatively large cross-sectional area at the end thereof adjacent said cavity and being closed at the end thereof remote from said cavity except for a relatively small perforation provided in said end remote from said cavity, said cavity and said hollow projection jointly forming a blown-fuse-indicator-receiving chamber;

b. a spring-biased blown fuse indicator arranged in said chamber;

c. a pair of substantially parallel conductor strips each arranged immediately adjacent to one of said pair of top and bottom walls;

(1. fuse link means conductively interconnecting said pair of conductor strips;

e. a fusible restraining wire for said blown fuse indicator entering through said small perforation into said hollow projection and having ends conductively connected to said pair of conductor strips;

f. a pulverulent arc-quenching filler inside said housing embedding said fuse link means and said restraining wire; and

g. fastener means securing each of said pair of conductor strips to one of said pair of top and bottom walls maintaining said pair of conductor strips in spaced relation by virtue of the spacing action of said fastener means and said pair of side walls in the absence of additional insulating spacers arranged within the space bounded by juxtaposed surfaces of said pair of conductor strips.

5. An electric fuse including a. a substantially prismatic housing of electric insulating material having a front wall, a rear wall, a pair of substantially parallel side walls and a pair of substantially parallel top and bottom walls, said front wall having a cavity in the front surface thereof and a hollow projection integral with said front wall aligned with said cavity, extending in cantileverlike fashion into the interior of said housing and being unsupported at the end thereof remote from said cavity, said hollow projection having a relatively larger cross-sectional area at the end thereof adjacent said cavity than at the end thereof remote from said cavity and being closed at said end remote from said cavity except for a relatively small perforation in an apex area of said projection, said cavity and said hollow projection jointly defining a blown-fuse-indicator-receiving chamber;

b. a spring-biased blown fuse indicator inside said chamber, said blown fuse indicator including to the exclusion of any additional part an indicating button, a helical biasing spring for said indicating button acting on one end thereof against said indicating button, a spring-supporting cap acted upon by the other end of said biasing spring, and a tie rod extending through said spring-supporting cap into said unsupported end of said hollow projection;

c. a pair of substantially parallel conductor strips arranged inside said housing at opposite sides of said hollow projection immediately adjacent to one of said pair of top and bottom walls of said housing;

(1. fusible means in ribbon form conductively interconnecting said pair of conductor strips and a fusible restraining wire entering into said hollow projections through said small perforation therein, attached to said tie rod at a point situated inside said hollow projection and conductively interconnecting said pair of conductor strips; and

e. a pulverulent arc-quenching filler inside said housing embedding said fusible means in ribbon form and said restraining wire.

* it a: s t 

1. An electric fuse including a. a pair of substantially parallel conductor strips; b. fuse link means conductively interconnecting said pair of conductor strips; c. a pulverulent arc-quenching filler embedding said fuse link means; d. a substantially prismatic casing of insulating material defining a chamber housing said pair of conductor strips, said fuse link means and said filler, one wall of said casing forming an integral hollow projection of progressively decreasing diameter extending in cantilever-like fashion into said chamber and being unsupported at the innermost end thereof, said hollow projection having a rounded apex at said innermost end thereof provided with a relatively small aperture, said one wall of said casing having a relatively large aperture juxtaposed to and aligned with said relatively small aperture; e. a spring-biased blown fuse indicator arranged inside said relatively large aperture of said one wall of said casing and inside said hollow projection thereof in the space between said relatively small aperture and said relatively large aperture; and f. fusible restraining means for said blown fuse indicator conductively interconnecting said pair of conductor strips and extending through said relatively small aperture into said hollow projection of said one wall of said casing.
 2. An electric fuse as specified in claim 1 wherein said relatively small aperture in said hollow projection is sealed by a body of sealing paste.
 3. An electric fuse as specified in claim 2 wherein said relatively small aperture in said hollow projection is sealed by a body of silicone grease.
 4. An electric fuse including a. a substantially prismatic housing of electric insulating material having a front wall, a rear wall, and a pair of substantially parallel side walls and a pair of substantially parallel top and bottom walls, said front wall having a cavity and a hollow projection integral with said front wall aligned with said cavity extending in cantilever-like fashion into the interior of said housing and being unsupported at the end thereof remote from said cavity, said hollow projection having a relatively large cross-sectional area at the end thereof adjacent said cavity and being closed at the end thereof remote from said cavity except for a relatively small perforation provided in said end remote from said cavity, said cavity and said hollow projection jointly forming a blown-fuse-indicator-receiving chamber; b. a spring-biased blown fuse indicator arranged in said chamber; c. a pair of substantially parallel conductor strips each arranged immediately adjacent to one of said pair of top and bottom walls; d. fuse link means conductively interconnecting said pair of conductor strips; e. a fusible restraining wire for said blown fuse indicator entering through said small perforation into said hollow projection and having ends conductively connected to said pair of conductor strips; f. a pulverulent arc-quenching filler inside said housing embedding said fuse link means and said restraining wire; and g. fastener means securing each of said pair of conductor strips to one of said pair of top and bottom walls maintaining said pair of conductor strips in spaced relation by virtue of the spacing action of said fastener means and said pair of side walls in the absence of additional insulating spacers arranged within the space bounded by juxtaposed surfaces of said pair of conductor strips.
 5. An electric fuse including a. a substantially prismatic housing of electric insulating material having a front wall, a rear wall, a pair of substantially parallel side walls and a pair of substantially parallel top and bottom walls, said front wall having a cavity in the front surface thereof and a hollow projection integral with said front wall aligned with said cavity, extending in cantilever-like fashion into the interior of said housing and being unsupported at the end thereof remote from said cavity, said hollow projection having a relatively larger cross-sectional area at the end thereof adjacent said cavity than at the end thereof remote from said cavity and being closed at said end remote from said cavity except for a relatively small perforation in an apex area of said projection, said cavity and said hollow projection jointly defining a blown-fuse-indicator-receiving chamber; b. a spring-biased blown fuse indicator inside said chamber, said blown fuse indicator including to the exclusion of any additional part an indicating button, a helical biasing spring for said indicating button acting on one end thereof against said indicating button, a spring-supporting cap acted upon by the other end of said biasing spring, and a tie rod extending through said spring-supporting cap into said unsupported end of said hollow projection; c. a pair of substantially parallel conductor strips arranged inside said housing at opposite sides of said hollow projection immediately adjacent to one of said pair of top and bottom walls of said housing; d. fusible means in ribbon form conductively interconnecting said pair of conductor strips and a fusible restraining wire entering into said hollow projections through said small perforation therein, attached to said tie rod at a point situated inside said hollow projection and conductively interconnecting said pair of conductor strips; and e. a pulverulent arc-quenching filler inside said housing embedding said fusible means in ribbon form and said restraining wire. 